My computer starts booting into Windows 2000 but won't go past the initial screen. I replaced the power supply and tried reinstalling the OS but it still won't boot into the OS. I have tried replacing the hard drive also and nothing doing. What should I do?

First try booting into Safe Mode. If it does, then you can make any necessary edits and then boot back into normal mode. Without more details, this is all I have for your right now.

Or you could try disconnecting all USB connections from the back of the PC and then try to boot into windows. Sometimes, when reinstalling windows, windows has not had time to detect the usb drivers yet and therefore locks the system when they are plugged in.

I don't know the computers current state so it is difficult to pin down the right solution from the information that you have given. I don't know if this is a new Windows install or an old install that just locked up on you one day. This is very important information.